Xfmrs' sized to whole load vs. separate load calc.

[Stripe]

Hello, I'm new to forum and was wondering if someone might be able to help me out. I'm on a 48-unit kitchenette conversion in a motel. The motel has different sections "A" and "B". They're fed from a Main 480v 1600amp MDP. with 400a and 600a bus duct feeders which run under the hallways. I've figured my loads to be added with demand factors that apply. I need 2 Xfmrs', 1 for each section. They'll be considered SDS' for the Main and subs I'll be adding. 1 off of the existing 600 amp duct section A and 1 straight off the MDP section B. My question is there are 16 units in one section and 32 in the other, when I figure the total connected load should I figure it for the 48 then divide it into one third for "A" and two-thirds "B" or separately for "A" and "B" for my Xfmr sizing.

 

[charlie b]

When calculating the load on any single feeder (i.e., on one transformer), include only the loads served by that feeder. There are demand factors that take into account the number of certain types of equipment. For example, if each unit has an 8 kW range, then one feeder (one transformer) will have 16 ranges, with a demand factor (from table 220.55, column B) of 28%. The other feeder would serve 32 ranges, with a demand factor of 24%. But if you used the total of 48 units, and then split the load 1/3 and 2/3, you would use a demand factor of 20%, and your answer would be low. So you have to treat the feeders separately.

Please note that if you are calculating the service to the entire building, that set of conductors will serve all 48 ranges. Therefore, it is appropriate to use the 20% demand factor for that part of the calculation

Welcome to the forum.